Recently, by multi-channel broadcast in proportion to digital satellite broadcast and cable television, video data obtained by a user greatly increase. On the other hand, because of progress in computer techniques and a realization of large capacity recording medium such as DVD, video data may now be stored as digital information and easily processed by the computer.
In order for the user to actually utilize the video data, an effective retrieval technique is necessary to retrieve the user's desired video from the large number of video data. As such kind of retrieval technique, some information is attached to each object in video data and the video data including the object matched with the user's necessary information is retrieved to supply audio-visual data to the user. In order to attach the information to the object in video data, processing to extract the object from the video is necessary. However, while the video data greatly increases, the user's manual operation to extract the object is not effective.
As for automatic detection technique of the object, a method to extract the object from video whose background area does not move is well known. However, in this method, it is assumed that the background area stands still. In case of moving the background area in proportion to moving the camera, it is difficult to detect the object from the video.
In short, if an outward form of the object is previously known but the background movement is not previously known, in case of retrieving the object by using the movement of the object, the retrieval is not correctly executed by effect of camera-work. For example, when an object moving to the left side is followed by the camera, the object almost stands still in a frame and the background moves to the right side in the frame. Therefore, the frame including the object moving to the left side is not retrieved from the video data.
As mentioned-above, in the prior art, the object is not correctly detected from the frame including the background relatively moving. Furthermore, the frame including such kind of object is not retrieved.